Inorganic Materials (v.45, #7)
Properties of amorphous Si1 − x Ge x :H (x = 0−1) films by B. A. Najafov; G. I. Isakov (711-716).
Plasma deposition has been used to grow Si1−x Ge x :H(x= 0 − 1) films, undoped and doped with PH3 or B2H6, for p-i-n solar cells and other optoelectronic applications. The optical, electrical, and photoelectric properties of the films have been studied at constant hydrogenation and doping levels. The films deposited under appropriate conditions are amorphous, and three-layer solar cells fabricated from such films offer an efficiency of 9.5% at an illumination of 100 mW/cm2. The photoresponse of the a-Si1 − x Ge x :H films strongly depends on Ge content. The hydrogen concentration in the films was controlled by varying the gas phase composition and was determined from the IR absorption in the films.
Crystal growth and physicochemical properties of structural analogs of krupkaite by V. O. Aliev; N. R. Akhmedova; S. M. Agapasheva; O. M. Aliev (717-722).
Single crystals of rare-earth analogs of the mineral krupkaite, CuPbBi3S6, have been prepared for the first time, and their physicochemical properties have been studied. The compounds CuYbBi3S6, CuEuEr3S6, CuYbEr3S6, and CuPbEr3S6 are isostructural with CuPbBi3S6 and crystallize in orthorhombic symmetry (sp. gr. Pb21 m, Z = 2): a = 11.204, b = 11.376, c = 3.960 Å (CuYbBi3S6); a = 11.244, b = 11.440, c = 3.998 Å (CuEuEr3S6); a = 11.30, b = 11.55, c = 4.03 Å (CuPbEr3S6); a = 11.236, b = 11.414, c = 3.98 Å (CuYbEr3S6).
Electrical conductivity of undoped and rare-earth-doped high-resistivity GaSe crystals by A. Sh. Abdinov; Sh. A. Allakhverdiev; R. F. Babaeva; R. M. Rzaev (723-727).
The time-dependent conductivity of nominally undoped and rare-earth-doped (N R≃10−5 to 10−1 at % Gd, Dy, or Ho) high-resistivity gallium selenide crystals has been measured under various conditions. At a relatively low applied voltage and T ≤ 150 K, the conductivity of the crystals reaches a steady-state value rather slowly. When a voltage above a certain threshold is applied for a long time at T ≤ 300 K, the material exhibits electric fatigue. An energy-band model is proposed which provides qualitative explanation of the results.
Synthesis and growth of TlInSe2 and TlGaSe2 single crystals by E. M. Godzhaev; S. R. Dzhafarova; K. D. Gyul’mamedov; E. M. Mamedov; S. S. Osmanova (728-730).
Methods of synthesis and growth of TlGaSe2 and TlInSe2 single crystals are developed. It is shown that the Bridgman-Stockbarger technique is efficient for growth of large TlGaSe2 single crystals, and zone recrystallization is efficient in the case of TlInSe2.
Etching of Zn x Cd1 − x Te by solutions of the HNO3-HBr-citric acid system by Z. F. Tomashik; G. M. Okrepka; V. N. Tomashik (731-736).
Chemical etching of CdTe single crystals and Zn x Cd1−x Te solid solutions by bromine-evolving etchants of the HNO3-HBr-citric acid system is studied. Projections of the surfaces of equal dissolution rates are plotted; the kinetics of etching processes and the influence exerted on it by the composition of solid solutions and initial concentrations of citric acid are found. The concentration limits of solutions for chemicody-namical polishing of surfaces of the mentioned semiconductors are determined.
Luminescent properties of Cd-In-Te solid solutions by I. N. Odin; M. V. Chukichev; M. V. Gapanovich; V. F. Kozlovskii; A. A. Nurtazin; G. F. Novikov (737-743).
The composition dependences of the unit-cell parameter for CdTe-based solid solutions in the CdTe-InTe and CdTe-In4Te3 joins have been used to determine the limits of the solid solutions. Magnetic susceptibility data and the measured and X-ray densities of the solid solutions suggest that CdTe doped with In2Te2 or In4Te3 contains In+ and In3+ on the cation site. The cathodoluminescence spectra of CdTe doped with In2Te2, In4Te3, and In2Te3 have been measured, and the effect of mixed heterovalent substitution (In+ and In3+) on the luminescence behavior of CdTe has been analyzed.
Thermal conductivity of Sb2Te3-Gd2Te3-Bi2Te3 solid solutions by R. A. Ismaiylova; I. B. Bakhtiyarly; D. Sh. Abdinov (744-747).
We have measured the thermal conductivity of Bi2Te3-Sb2Te3-Gd2Te3 solid solutions at temperatures from ∼80 to 300 K and have determined the electronic and lattice components of their total thermal conductivity and the contributions of Sb2Te3 and Gd2Te3 to their thermal resistance. The results indicate that heat in these materials is transported largely by phonons and that three-phonon processes play a key role in determining the lattice thermal conductivity of the solid solutions.
Synthesis and investigation of superconducting properties of heterosubstituted magnesium diborides by L. G. Sevastyanov; P. E. Kazin; O. V. Kravchenko; O. K. Gulish; M. E. Leonova; V. A. Stupnikov; V. K. Genchel’; B. M. Bulychev (748-753).
The properties of magnesium diborides with the composition Mg1 − x M x B2, where M = Al, Ga, In, and Tl, and Mg (B1 − x E x ), where E = N, P, and Si (0.05 ≤ x ≤ 0.3), made by sintering of calculated amounts of boron, magnesium, and a substituent element or by a solid-phase exchange reaction of a corresponding halogenide of a metal with MgB2 at 1070–1170 K are studied. Using RFA technique, it is shown that, from all employed heterosubstituents, only the atoms of aluminum, gallium, and silicon in the amount x ≤ 0.2 are incorporated into magnesium and boron sublatticies. Here, the temperature of the superconducting transition T c = 39 ± 1K determined for pure magnesium diboride hardly changes.
Phase relations in the LaB6-W2B5 system by S. S. Ordan’yan; D. D. Nesmelov; S. V. Vikhman (754-757).
The LaB6-W2B5 join in the ternary system La-B-W is shown to have a eutectic phase diagram with t e= 2220°C and a eutectic composition of 30 mol % LaB6 + 70 mol % W2B5. Data are presented on LaB6-containing systems potentially attractive for designing mixed-phase ceramics.
Preparation of silicon carbide whiskers from silicon nitride by Yu. F. Kargin; S. N. Ivicheva; A. S. Lysenkov; N. A. Alad’ev; S. V. Kutsev; L. I. Shvorneva (758-766).
Silicon carbide whiskers have been prepared by sintering silicon nitride powder in a graphite reactor at 1800°C under a nitrogen atmosphere. The whiskers differ in morphology: tubular needles, hollow faceted fibers with a square cross section, and solid fibers with a triangular cross section. The average diameter of the needles is 0.5−5 μm, and that of the faceted fibers is up to 20 μm. The fibers range in length up to several millimeters. Such silicon carbide whiskers can be used as reinforcing agents for structural ceramics based on nonoxide materials.
Synthesis of nanostructured Pt x Ni/C and Pt x Co/C catalysts and their activity in the reaction of oxygen electroreduction by A. V. Guterman; E. B. Pakhomova; V. E. Guterman; Yu. V. Kabirov; V. P. Grigor’ev (767-772).
Nanostructured Pt x Ni/C and Pt x Co/C catalysts (1 ≤ x ≤ 3) containing from 27 to 40 wt % of metal with the average size of metal (alloy) particles from 2.6 to 4.7 nm are obtained using the methods of liquid-phase synthesis. Addition of a doping component is found to yield a decrease in the average nanoparticle sizes and an improved activity of materials in oxygen electroreduction reactions. The obtained catalysts are characterized by high specific activity as compared to commercial Pt/C materials. The stability of electrocatalysts to selective dissolution of the doping component is evaluated.
Preparation of TiSi2 via flash lamp processing of TiN/Ti/Si heterostructures by V. M. Ievlev; S. V. Kannykin; V. V. Kolos; S. B. Kushchev; M. I. Markevich; A. M. Chaplanov; V. F. Stel’makh (773-776).
The structural and phase transformations induced in the TiN/Ti/Si system by flash processing with incoherent light have been studied by transmission electron microscopy and Auger electron spectroscopy. The conditions have been identified under which polycrystalline C49 or C54 TiSi2 films grow.
Production of intermetallic catalysts of deep CO and hydrocarbon oxidation by V. N. Sanin; D. E. Andreev; E. V. Pugacheva; S. Ya. Zhuk; V. N. Borshch; V. I. Yukhvid (777-784).
The possibility of producing (Ni, Co, Mn) Al x intermetallides using the technique of self-propagating high-temperature synthesis and their subsequent processing with the purpose of using them as catalysis in the process of complete oxidation of CO and hydrocarbons is considered. Phase composition, microstructure, and morphology of alloys and catalysts based on them are studied. Dependences of activity and stability on composition are determined. These catalysts are shown to possess high activity and their development is considered to be a promising direction in the catalysis of deep oxidation processes.
Emission spectra of silver-infiltrated opal photonic crystals under excitation through optical fibers by V. S. Gorelik; L. I. Zlobina; O. A. Troitskii; R. I. Chanieva (785-790).
The emission spectra of opal photonic crystals loaded with silver nanoparticles have been measured in a 180° geometry under UV and visible excitation. The spectra of silver-infiltrated opal under excitation through optical fibers are found to differ from the spectra of plain (uninfiltrated) opal: the infiltrated silver shifts the emission maximum to longer wavelengths and changes the shape of the spectrum. We have calculated the dispersion laws for two photonic bands and the corresponding frequency dependences of the refractive index for the photonic crystals studied.
Effect of the chemical heat treatment in a semianthracite char on the chemical composition by M. Alfaro Domínguez (791-794).
The effects of chemical heat treatments of a semianthracite char (AC) on the composition of the mineral fraction of the material are investigated. Sample AC was first treated with a mixture of LiCl/KCl or a mixture of LiCl/KCl and a metallic oxide, M n O (MgO, CaO, FeO, CoO, NiO, Cu2O or ZnO), at 743, 873 or 1173 K and the products obtained were then washed thoroughly with distilled water. The composition changes were studied by X ray diffraction. The predominant mineral components initially present in the starting char are quartz, mullite, muscovite and/or kaolinite and oldhamite. The treatments of AC resulted in significant changes in the mineral fraction of the material, in particular when the mixture LiCl/KCl/MgO or LiCl/KCl/CaO was used for the highest temperature, 1173 K.
Electrical and thermodynamic properties of Cs0.97 Rb0.03H2PO4 by G. V. Lavrova; V. V. Martsinkevich; V. G. Ponomareva (795-801).
The transport properties of Cs0.97Rb0.03H2PO4 have been studied using polycrystalline samples and single crystals. The mixed salt is isostructural with cesium dihydrogen phosphate and has slightly smaller unitcell parameters. The cation substitution increases the low-temperature ionic conductivity of the material by about two orders of magnitude but has an insignificant effect on the conductivity of the high-temperature phase. The low-temperature conductivity of single-crystal samples exhibits significant anisotropy, with σ a < σ b±c . The conductivity of the polycrystalline material is close to σ b±c . The substitution reduces the temperature of the superionic phase transition by 20°C and enhances the thermal stability of the high-temperature phase at low humidity (1 mol % H2O).
Stability region of Gd2 − x Mn x O3 ± δ solid solutions in air by O. M. Fedorova; V. F. Balakirev; Yu. V. Golikov (802-805).
The solid-solution range of Gd2 − x Mn x O3 ± δ has been determined using X-ray diffraction analysis of samples with 0.90 ≤ x ≤ 1.20 (Δx = 0.02) prepared from oxide mixtures by solid-state reactions in air between 900 and 1400°C. The results have been used to construct a partial phase diagram of the Gd-Mn-O system in air. It is shown that gadolinium manganite with the perfect metal stoichiometry, GdMnO3 ± δ, does not exist. The material of this composition in air consists of two phases: a Gd2 − x Mn x O3 ± δ solid solution with an orthorhombic perovskite-like structure and the binary oxide Gd2O3. The solid solution extends to the composition Gd0.96Mn1.04O3 ± δ. Over the entire temperature range studied, gadolinium oxide does not dissolve in Gd0.96Mn1.04O3 ± δ. Mn3O4 exhibits significant solubility in Gd2 − x Mn x O3 ± δ. In particular, Gd0.86Mn1.14 O3 ± δ is single-phase by X-ray diffraction in the temperature range 1185–1400°C. Below 1185°C, Gd2 − x Mn x O3 ± δ is in equilibrium with another gadolinium manganite, GdMn2O5. With decreasing synthesis temperature, the GdMn2O5 solubility in Gd2 − x Mn x O3 ± δ drops precipitously. At 900°C, the only single-phase sample was Gd0.96Mn1.04O3 ± δ.
Structure and properties of the layered compound HoBaCuCoO5 + δ by A. I. Klyndyuk (806-808).
HoBaCuCoO5 + δ has been synthesized, and its crystal structure and physicochemical properties have been studied. It crystallizes in tetragonal symmetry (sp. gr. P4/mmm) with lattice parameters a = 0.3867(2) nm and c = 0.7554(5) nm (V = 113.0(2) × 10−3 nm3, δ = 0.01) and is a p-type semiconductor. According to dilatometry results, holmium barium cobaltocuprate undergoes no structural phase transitions in the temperature range 300–1100 K. Its linear thermal expansion coefficient is 15.1 × 10−6K−1.
Chemical interaction of fluoropolymers with transition metals by A. V. Tarasov; A. S. Alikhanian; I. V. Arkhangel’skii (809-813).
Chemical interaction of transition metals (Mo, W, Ta, Nb, and Ti) with a tetrafluoroethylene-vinylidene fluoride (TFE-VDF) copolymer (21 mol % TFE + 79 mol % VDF) has been studied by differential scanning calorimetry (DSC) and mass spectrometry. The DSC curves of mixtures of the fluoropolymer with Ta, Nb, and Ti showed exothermic peaks, and those of composites with W and Mo showed endothermic peaks. Mass spectrometric analysis indicated that the fluoropolymer reacted with the transition metals to form the higher fluorides TaF5, NbF5, TiF4, WF6, and MoF6. In addition, WOF4 and MoOF4 molecules were detected in the case of tungsten and molybdenum. At temperatures above 700 K, the mass spectra of all the systems showed ions corresponding to low-molecular hydrocarbon molecules.
Deformation, polarization, and reversible properties of lead-free ceramics based on alkali metal niobates by I. A. Verbenko; O. N. Razumovskaya; L. A. Shilkina; L. A. Reznichenko; K. P. Andryushin; V. V. Kiselev (814-822).
We have studied the deformation, polarization, and reversible characteristics of [(Na0.5K0.5)1 − x Li x ](Nb1 − y − z Ta y Sb z )O3 ceramics, and examined the effect of an applied electric field on their properties. Property-structure-composition relationships have been inferred, and the influence of CuO + TiO2, CaO, CdO, and SrO + TiO2 additions has been assessed. The results are interpreted in terms of the defect structure of the ceramics and domain wall mobility. The most attractive materials for microwave applications and dielectric amplifiers are identified.
High-aperture optical waveguides based on fluorine-doped silica glass by A. N. Guryanov; M. Yu. Salganskii; V. F. Khopin; A. F. Kosolapov; S. L. Semenov (823-826).
The dependence of fluorine incorporation into silica glass on conditions of the optical waveguide blank manufacture using the method of modified chemical vapor deposition (MCVD) is studied. The degree of fluorine incorporation at constant consumption of a fluoridizer (SiF4) is shown to increase with an increase in the volume of deposited material. Samples of multimode optical waveguides with a core from pure silica glass and a reflective coating made of fluorine-doped silica glass with a numerical aperture of ∼0.18 are obtained. Optical losses in such optical waveguides reach 0.5 dB/km in the long-wavelength region of the spectrum.
Obtainment of the Fe0.70−x Cr x Al0.3/Al2O3 nanocomposite by the method of SHS of mechanoactivated Cr2O3 + Fe + Al mixtures by T. Yu. Kiseleva; A. A. Novakova; T. L. Talako; T. F. Grigor’eva; A. N. Falkova (827-831).
Applying Mössbauer spectroscopy methods, we have studied the structure of nanocomposites obtained by a technique combining the preliminary mechanical activation of an 8.1 wt % Cr2O3 + 65.9 wt % Fe + 25 wt % Al mixture and self-propagating high-temperature synthesis (SHS). It has been found that, at the stage of mechanical activation, an Fe/Al/Cr2O3 composite with a low impurity of the Fe2Al5 intermetallide is formed. At the stage of SHS, the interaction between activated components of the mixture leads to the formation of the Fe0.7 − x Cr x Al0.3 (x = 0 − 0.2)/Al2O3 composite.